Traveling wave tube



5 Shets-Sheet l IIN July 28, 1959 Filed April `21, 1955 July 28, 1959 A. w. FRIEND 2,897,397

TRAVELING WAVE TUBE Filed April 21, 1955 3 Sheets-Sheet 2 INVENTOR. ALBERT W. FRlEND ATTORNEY July 2s, 1959' Filed April-V21, 1955 (SL T)x Ioo E A. w. FRIEND 2,897,397 :IRAVELTNG WAVE TUBE PERCENT GREATER PowER ..7 REQUIR'ED BY I AYER wouND soLENoID con. THAN BY EDGE 55 wouND soLENoID con..

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ALBERT w. FRIEND ATTORNEY TRAVELING WAVE TUBE Albert Wiley Friend, Bala-Cynwyd, Pa., assignor, by mesne assignments, to Sylvania Electric Products inc., Wilmington, Del., a corporation of Delaware Application April 21, 1955, Serial No. 502,763

1 Claim. (Cl. S15-3.5)'

The present invention relates to a method and yapparatus for the continuous production of edge-Wound metallic helices and in particular is concerned with an improved method for manufacturing electromagnetic focusing coils for traveling wave tube amplifiers and like devices, and to improvement in the physical and operational characteristics of such devices.'

In the manufacture of electrical conductors and components it has long been known to produce impurity free Wires by a process of electrodeposition which involves the plating of metal onto a traveling cathode surface and the stripping of the metal from said cathode surface. For example, in the manufacture of thin metal foils, it is commonplace to support a drum-like cathode such that a portion of its periphery is immersed within an appropriate electrolyte containing the metal ion. In operation the metal is deposited on that peripheral portion of the cathode which is immersed in the electrolyte or plating solution and as the cathode rotates, a deposit builds up to a desired thickness. Mechanisms are provided for continuously stripping the deposited metal from the periphery of the cathode and for rolling the foil up in any convenient manner. The metal foil so produced may be of gold, silver, copper, nickel or any metal or alloy which may be electrochemically deposited on a cathode.

It is broadly an object of the present invention to provide an improved method and apparatus for electroforming a thin, continuous metallic strip. Specically, the present invention is concerned with the formation of an edge-wound helix of deposited metal including successive flat surfaced turns spiraling about a reference line with the fiat surfaces of the turns substantially at right angles to the reference line.

Certain aspects of the invention may be best appreciated by considering its application to the manufacture of traveling Wave tubes and like devices containing one or more electron beams which must be confined to flow within accurately defined boundaries. Such traveling wave tube devices usually include an electron gun, similar to those commonly found in cathode ray tubes, which forms and projects an electron beam axially within a metal elecfrode assembly arranged concentrically of and within a vitreous supporting envelope. The electrode assembly includes an input probe, an output probe spaced from the input probe and a helical conductor or coil connected between the probes. An input signal is supplied to the input probe and during travel along the helical conductor interacts with the electron beam, resulting in amplification of a broad band of input frequencies which are extractable at the output probe of the electrode assembly. There are two principle types of electron guns which may be used to provide the desired electron beams. In the parallel flow type of gun, the axial magnetic field passes through the gun land guides the electron along the field as the electrons leave the cathode, pass through the electron gun and travel down the electrode assembly. In the converging or conical ow type of gun, the emitted electrons are converged by electrostatic Patented July 28, 1959 fields which produce a dense beam of axially moving electrons at an external plane where the beam abruptly enters into an axial magnetic field Which then serves to maintain the beam in focus during its passage through the electrode assembly. Beam focus in either instance may be obtained by a large single permanent magnet or by a solenoid. For certain applications, including very high current density and high voltage beam of medium and high power traveling wave tubes, it is essential to employ electromagnetic focusing structures to furnish very strong magnetic fields to produce adequate focus.

Solenoids heretofore employed, have usually included a `spool having an inside diameter appropriate to slip over the supporting envelope of the electrode assembly or over the gun in the case of the parallel fiow arrangement. The spool has Wound thereon a great many turns and layers of appropriate magnet Wire. When employing such solenoids, it is important that the winding be applied in a uniform manner to assure uniformity in the focusing field `and that the supporting spool be sufliciently rigid to avoid deviation of the electron beam from the desired axial path of travel. As a practical matter, such solenoids have been found to be quite heavy and capable of producing only relatively weak magnetic fields. Further, the fields ofsuch solenoids have been found to extend to surrounding spaces, thus requiring shielding to preclude interference with the function of adjacent electronic apparatus,

Attempts to obtain higher field strength with such structures have led to excessive heating of the Winding and the need for forced cooling. In an attempt to construct lightweight, high field strength solenoids with capacity to remove heat produced as a result of the elec.- tric cunrent required to produce the high field strength, it has been suggested that the solenoid take the form of a layer of wound foil of one turn per layer. This approach appears to be an improvement over the `conventional wire-wound solenoid, which has a very poor path for the conduction of heat to the outer surface, in that heat may be extracted from the edges of the successive layers. However, as a practical matter, the layer wound arrangement falls short of an optimum structure which is of low mass, lightweight and capable of producing high field strengths of low power consumption and with minimum cooling problems.

Accordingly, it is a further object of the present invention to provide an improved solenoid for focusing an electron beam. Specifically, it is Within the contemplation of the present invention to provide improved traveling wave devices of high power having light, and high field strength solenoids for focusing the electron beam of the device.

In accordance with this illustrative aspect of the invention, there is provided in combination with a traveling wave tube including an electron gun for projecting -a beam of electrons along a predetermined path, an electromagnetic focusing means which surrounds said path and includes an edge-wound metal helix.

The use of such edge-wound helix solenoids for electromagnetic focusing offers numerous advantages, particularly when compared to comparable layer-wound coils of either wire or foil. Outstanding among these advantages are the substantial reduction in required electric power (see Fig. 8), the ease of conduction of heat radially to the outer periphery of the solenoid across the radial extent of the respective turns, and the further heat conduction path afforded along the entire inner and outer cylindrical surfaces of the edge-wound helix. Apart from the substantial reduction of maximum winding temperature and the reduction of the weight of the solenoid, its power source and its cooling system, the edgewound helix may be supported entirely from the outside surface. vThis facilitates reduction-ofthe -inner diameter of the solenoid to one fitting closely over the traveling wave tube, thus further contributing greatly to red'uotion Yin flsize, weight? and 'required loperatingpower, since, to maintain@ lthesa'me powerJv inputf wheni fthe insidedi'aineter 4iisbhangeifthe ratio 12/ r1 "of buter'toinner radismust'be :maintained constant. Y

The ed'g'efwinding ofhelices 1'embodying lfe'atures of the pres'entfnvention by known mechanical 'forming -techniques `is especially diiiicult, particularly 'if `the radial widthof the helix is large compared to f the thickness olf/theA respective helix tur-ns, 'or-'whentthe inside windig'fdameter is small-in comparison 'to'the radial extent of the turns. In accordance with further1 aspects ofthe prsentinvention, 'the edge-'Wound h'elixis ffoimed by legctoforming orvacuum 'evaporation processes.

The above objects, `brieffclescriijition carl1d`-still ffurther features and advantages-ofthet-prese'nt invention will be best appreciated byreferen'ce toithe'fllowingdetailed description of presently "tpeferred apparatus, processes, and devices embodyingfeatures'lof theinvention, when taken in conjunction v'vith'itheA accompanyinglfdrawings, wherein:

Fig.' l is 4an elevational view of `anedge-vvound focusing-solenoid according tothe present-inventionjshown surrounding a `traveling vwave tube device incorpora-ting a parallel llow electron gun;

Fig. 2 is an elevational View of anedge-Wound 'focusing solenoid according to the-present "invention, shown -surrounding a traveling Wave ltube device incorporating a converging flow type of electron gun;

Fig. 3 is a fragmentary perspective view ofv thehelix assembly of Fig. 1;

Fig. 4 is a 4fragmentary 'perspectiveview of a segment of the helix of Fig. 3 lwith the respective turns spread apart;

Fig 5 isa :fragmentary elevational view,"with parts broken away and sectioned forthe purpose of clarity,` of -the spread=apart helix of Figj 4;

Fig. 6 is a somewhat schematic elevational showing ofpreferred apparatus for preparing ele'ctroformedl 'edgewoundheliceg p Fig. 7 is a plan view of a rotatable cathode'disc incorporated'in the apparatus'ofFig. 6; and

`Fig. r8 is agraph'showing in percentages the power requirement `for a layer wound solenoid coil'as compared :toan' edge-Wound solenoid'coil for the same coil space factor, conductor materials, size and shape. p Preliminary 'to a detailed discussion of the illustrative embodiments, process and 'apparatusset forth 'herein- "after,- all of which apply specifically ,tofocu'sing coils for the-electron beams of traveling wave' tube devices, it is to be vstressed that the process and' apparatus 'of the pres- =ent invention, and coils obtained according to the present invention, find more generalized application. 'How- "ever, in that 'the various features of lthe invention 'may best befillustrated and find exceptionally important application 'in the `construction of traveling wave tubes, the description `"hereinafter will be specifically directed to this aspect of the invention. In Fig. l there is shown an illustrative 'traveling Wave tube 10 whichincludes a vitreous body lzhaving an enlarged bulb end 14, and an elongated slender sleeve or'tube 16. Within the bulb or enlarged Vend 14 is the welllnown parallel flow gun assembly 18 which is arrangedto produce a beam to be axially directed along thersleeve '16. Within thesleeve 16 isan electrode assembly'including an input probe 20, afhelical conductor '22 of uniform or variable pitch' having one end velectrically connected to the input probe 20, :and-an output probe 24 electrically xconnected to =the1fother end@ of :the helix: 'Beyond-the output probe `Z4 is :a`colle'ctor (not shown) Afor `.the'electron Ybeams-having appropriate ext'einalV connections. As 'is JWellZurrderstood, operatingpov4 tentials are provided to the several components of the traveling wave tube.

In accordance with one aspect of the present invention, the traveling wave tube envelope including the bulb end 14 and the sleeve 16 containing the electrode assembly is enveloped 'within an electromagnetic focusing device 30 including an edge-wound helix 32 having successive tial; surfaced turnsLBQa of uniform pitchzspiraling about a reference line concentric with the beam axis, with the flat surfaces of the respective turns at ysubstantially right angles to the reference line. The edge-wound .helix 32 is of deposited metal, prepared by electroforming or vacuum deposition. f Materials suitable for the edge-wound helix include copper, which may be plated out of a somewhat conventional and easily handled electrolyte containing the copper ion, or aluminum, which may be plated out from an anhydrous bath of organic chemical nature. Separating the respective turnsof the-cdgewound -helix '32 iseinsulation=34 which-may take the form=of `an oxidized metal surface of the helix itself,synthetic, organic or silicone coatings formed on the helix or fused vitreous coatings.

The -helical coilV 32 with the insulation 34, is clamped together with the respective turns in abutting -relation Vand-of uniform spacing throughout the length of the coil by the use of fcrromagncticeitidy platcs, 38 which also serve as the pole pieces of the magnet. An outer ferromagnetic 'cylinder 40 is connected between the respective end plates 36, v38 yand if desired, `may serve as a tensioning `memberand a cooling-airretainen As seen in Fig. l,-=there is an annular-space42 about `the outer peripheryfof the helical `coil B2 in-Iwhichcooling air may |be confined for rextracting-the heat from'each vindividual turn of -the lhelix 1through theI many -radialv conducting paths vafforded bythehelix turns which extend from the innerperiphery -of the coil to the youter periphery. Additionalcooling air maybe `passed'longitudinally through 'the solenoid bore-and around the ytraveling wave tube envelope 12to cool the tube andthe inner periphery of thecoil.

"In Fig. 2, there is shown a further application ofthe edge-wound yfocusing helix as specifically applied to a traveling 'Wave tube "50 incorporating a converging or conicaly fflowftypefof 'gun 52. lAs is -well understood in the art, -this type of'ggun produces a dense beam of axially moving lelectrons' atan external plane where the beam shouldfabruptly xenter into `an axial magnetic focusing-field. This magnetic ieldunaintaius'the beam in focus during its passagethrough the high frequency interaction structure. To this end, al1-electromagnetic focusing device Sty-*Which is Iessentially the-same as the Vfocusing zdevice -134i, -'envelopes the 'slender tubing VL54, of the ltraveling wave --tube udevicet?, v but vdoes not extend vabout'the gun"52. PlatesS, y58 `which serve as shields `and lsupports for Athe tubefenvelopef54, are seated -within the'end .plates36'-,"38 of-the yfocusing coil-30'. Plate 56 -mayform `a portion offthevacuum lenvelope of the tube.

In either of the forms-illustrated in Figs. l and 2, the edge-wound Ahelical solenoid-provides an essentially -uni form magnetic 'Heli-:thus assuring yuniform` focusing and smooth 1ow of 'the 'electron'beam- The edge-wound f helicalfsolenoid yisfieminently suitable for-the-prov-ision of strong magnetic-'field :required to focus the -highcurrent'y density-f;*high-voltage beam of medium and lhigh power traveling wavetubes.

yInl^Figs; 3 lto 5 inclusive, there is shownan edget 'wound-helix A32 fwhich isv incorporated in the focusing 'the helix. The inner bore diameter may be selected to lit snugly about the 'bulb end 14 of the traveling wave tube envelope 12, as illustrated in Fig. 1. In the alternative, the inner diameter of the helix may be selected to fit with clearance about the sleeve 50 of the traveling wave device 54, as illustrated in Fig. 2.

In accordance with a preferred form of the present invention, the helix illustrated in Figs. 3 to 5 and incorporated in devices of the type shown in Figs. l and 2, s electroformed by apparatus shown in Figs. 6 and 7. Such apparatus is seen to include a tank or container 60 containing a plating solution P to a predetermined level L. Extending into the plating solution P is an anode 62 connected by a lead 64 to an appropriate plating supply. Disposed in a plane inclined to the horizontal and to the level or surface L is a rotatable cathode disc 66 including a planar face 68. The cathode disc 66 is supported on a shaft 70 driven at constant speed by a motor 72 energized from an appropriate source (not shown). The planar face 68 of the rotatable cathode disc 66 is stopped oif as indicated at 74, 76 to provide an exposed annular band 68a of the annular sunface 68. As is well understood in the art, the exposed surface 68a is electrolytically treated and highly polished to place it in condition for continuous non-adherent plating and continuous clean stripping. Disposed at an angle to and spaced above the rotatable disc 66 is a storage device 78 which includes a mandrel 80 and a drive motor 82. The mandrel 80, which is constructed to accommodate successive turns of the helix as the same are stripped from the cathode 66, is driven by the motor 82 at a speed synchronized to the rotation of the cathode 66 such as to receive successive turns of the helix.

In practicing the electroforming of the helix, the rotatable cathode disc 66 is fabricated of stainless steel. Preliminary to setting up the apparatus of Fig. 6, the cathode is passivated by making the same an anode in a hot alkaline electrocleaning solution. This treatment removes oily matter from the stainless steel cathode in addition to forming a thin passive film which prevents adhesion of the electroformed metal during plating and assures continuous clean stripping. Following the anodic treatment, the stainless steel cathode is rinsed in water to remove the alkaline solution. Of course care must be exercised to prevent abrasion of the surface subjected to passivation, which abrasion would tend to destroy the passive film and result in the adhesion of plated metal. If the metal helix is to be of copper, a suitable electrolyte is an aqueous solution containing approximately 336 grams per liter of copper uoborate. Such electrolyte may be operated at a pH of between .5 and .7 with vigorous agitation with a copper anode operating at a bath temperature of 90 F. With a plating current of approximately 5 amperes, it is possible to form approximately six helix turns per hour having an outer diameter of three inches, an inner diameter of one inch, and a thickness of .002 of an inch.

As seen in the schematic showing of Fig. 6, approximately a one-half segment of the rotatable cathode surface 68a is immersed in the plating solution P. It has been found that the exposure to air of slightly less than one-half of the cathode surface during each revolution is an aid to maintaining the passive character of the cathode surface. Of course, it is to be understood that the details of the electroforming operation are subject to a latitude of variation within the skill of those in the art. The deposited metal helix has its respective turns insulated from each other, for example, by the application of synthetic, organic or silicone coatings to one of the continuous spiraling surfaces.

The present method may be used for the purposes of plating aluminum into a continuous edge-wound helix by the use of an appropriate anhydrous bath. For 'a description of the techniques of electrodepositing aluminum, reference may be made to an article by D. E. Couch and A. Brenner entitled Electrodeposition of Aluminum appearing in The Journal of the Electrochemical Society, vol. 99, No. 6, pages 234 to 244 of June 1952. When the deposited metal helix is of aluminum an insulating layer between the respective turns is provided by anodizing the aluminum helix. Such anodizing, which may be achieved in accordance with known techniques, results in a tough adherent insulating coating on the surface of the aluminum for isolating the respective turns. n

It is likewise within the contemplation of the invention to deposit the metal of the edge-wound helix, and its insulation by a continuous vacuum evaporation and deposition method. Such methods are well known to the art of manufacturnig lenses having thin continuous metallic coatings and accordingly will not be detailed herein. Accordingly, the term deposited employed in the appended claims should be afforded a latitude of interpretation consisting with the electroforming or cathode depositing of the metal of the helix or the vacuum depositing of such metal onto a rotating annular surface.

From the foregoing, it will be appreciated that edgewinding of the successive turns of a solenoid allows for the design of the focusing coil for an electron beam of lower power consumption than comparable layer winding of wire or metal coil. Further, edge-wound solenoids allow for maximum heat dissipation per unit volume in comparison with layer wound foil and wire coils, and in particular facilitates the application of refractory insulating materials, as by spray coating or by rendering surface areas non-conductive. Still further, edge-wound solenoids facilitate obtaining and maintaining a uniform current distribution along the solenoid axis in that the pitch of the successive turns may be controlled to great accuracy by precision deposition of the metal followed by careful assembly. Still further, a uniform axial field may be obtained with an edge-wound solenoid in that no serious problem is encountered in termination of the conductors. This is an important advantage as compared to the broad layer wound coils which must include a current lead to the inner turn, the current lead being coaxial with the electron beam and in good contact with the foil along its length to minimize stray currents which may produce spurious transverse magnetic field and poor focusing throughout the length of the beam. Still further, edgewound helices provide a means for obtaining comparatively low system weight and power consumption, of prime importance in air-borne application of traveling wave devices. For a comparison of power requirements for a layer wound coil and a comparable edge wound coil reference may be made to the graph of Fig. 8.

Further modifications and various applications of the foregoing invention will occur to those skilled in the art, and accordingly the appended claim should be construed broadly, as is consistent with the spirit and scope of the present invention.

What I claim is:

In a travelling wave tube, an electron gun for producing an electron beam; a collector electrode for collecting said beam; a first helix constituted by electrically conductive material and interposed between said gun and said electrode, the axis of said first helix being coincident with the path of said beam; and a second helix constituted by an electrically conductive continuous metal ribbon surrounding said tube in the region of said first helix, said second helix having an inner diameter substantially greater than the outer diameter of said first helix, the axis of said second helix being coincident with that of said first helix, the edges of said ribbon being transverse to the axis of both helices, the surfaces of said ribbon being electrically non-conductive.

(References on following page) 'References Cited in -the le of this patent UNITED STATES PATENTS Edison Feb. 25, 1908 Edison May 23, 1922 5 Fritz 2 Aug. 9, 1932 .VorrVedel O ct. 10, -1933 Yates A ug. 25, 1936 `Sehwartz Iuly-12, 1938 Knoll Sept. 27, 198 l0 j Von Ardenne Jan. 2, 1940 Yates Sept 21, 1943 Dewey' Jan.,10, 1956 Sam'eI .Aug. 7, 1956 A Clarke Aug. 21,1956 Pierce May 14, 1,957 Haeff Sept. 10, y1957 

